The present invention is generally related to expansion valves and more particularly to thermal expansion valves where the direction of fluid flow therethrough is reversible.
Thermal expansion valves are generally used in systems employing heat pumps. In a heat pump system refrigerant flow is typically reversible. In this manner, the heat pump can be utilized to provide heating in cold weather and cooling in warm weather. To accomplish this, these systems generally employ two heat exchangers commonly referred to as coils. The coils used are an indoor coil and an outdoor coil each of which depending on whether the heat pump is operating to provide cooling or heating, can function as either a condenser or an evaporator. To facilitate proper operation of the heat pump system each of the coils typically has a thermal expansion valve coupled thereto.
Generally, when operating in a cooling mode, a compressor in the heat pump system forces refrigerant to a reversing valve. The refrigerant flows from the reversing valve to the outdoor coil which acts as the condenser. The refrigerant then flows from the outdoor coil through an expansion valve to the indoor coil which acts as the evaporator.
Typically, thermal expansion valves have a relatively small expansion orifice through which the refrigerant must flow in order to enter the cooling coil. As such, thermal expansion valves have historically been single direction. In reverse flow situations, an attempt to force refrigerant through the expansion orifice would unduly restrict flow. Accordingly, prior art heat pump systems were provided with an external bypass line that incorporated a check valve. In reverse flow situations, the refrigerant would flow through the bypass line and the check valve, which allowed fluid to pass therethrough in only one direction.
The separate check valve and bypass line often required field installation and multiple plumbing joints, thereby increasing installation expense, as well as maintenance costs. In addition, the potential for leaks also increased due to the added piping involved to connect the bypass line and the check valve to the heat pump.
In an effort to obviate the problems associated with external bypass lines and check valves, expansion valves incorporating internal check valves have been manufactured. However, these internal check valves typically employ multiple components including spring-loaded balls or plungers. Some known check valves have employed flapper valves. A flapper valve is typically gravity dependent and must be positioned in the proper orientation. Usually if mounted in an upright or sideways position, fluid pressure is required to maintain the flapper in a closed position. When mounted upright, gravity acts against the fluid pressure to keep the valve open. Therefore, if the heat pump is operated under low pressure, there is the potential for more pressure acting on the valve pushing it open, thereby making it impossible to maintain the valve in a dosed position. Because the check valve cannot be maintained in a dosed position, it becomes difficult to control expansion of the refrigerant through the valve.
Another difficulty occurs when the above-described valve is under high pressure. In this situation, there is a time lag between the start of high-pressure flow through the expansion valve and the closing of the flapper valve. During this time period the valve remains open and refrigerant can flow through the bypass line making the expansion valve difficult to control.
In valves wherein the check valve incorporates a spring-loaded ball positioned in a bore machined into a valve body, machining the bore can be difficult. Since the valve body is small and of a shape that does not easily render itself to precise positioning, complex fixtures are required which increase manufacturing time and cost. In addition, assembly of the components of the check valve adds to the overall complexity of the valve assembly. This further exacerbates the problems of increased manufacturing time and cost.
Based on the foregoing, it is the general object of the present invention to provide an expansion valve that improves upon or overcomes the problems and drawbacks associated with prior art expansion valves.
The present invention is directed in one aspect to an expansion valve that includes a valve body having an inlet and an outlet. An expansion orifice is defined by the valve body and is in fluid communication with the inlet and the outlet. A closure is positioned in the valve body and is movable between an opened and a closed position. When in the open position, the closure allows fluid to pass through the orifice from the inlet to the outlet. When in the closed position, of the closure blocks the orifice thereby preventing fluid from flowing between the inlet and the outlet.
The valve body also defines a bypass flow path that is in fluid communication with the outlet and the inlet. A bypass closure is positioned in a free floating manner in the bypass flow path and is also movable between an opened and a closed position. When the closure is in the closed position, and the flow of fluid is through the outlet, towards the inlet, commonly referred to by those skilled in the pertinent art to which the invention pertains as xe2x80x9creverse flowxe2x80x9d, pressure exerted by the flowing fluid against the bypass closure causes it to move from its closed position towards the open position. This allows fluid to pass from the outlet to the inlet. Conversely, when the closure moves from the closed position toward the open position, fluid flows from the inlet, through the expansion orifice, to the outlet. In this situation, fluid pressure is exerted against a rear surface of the bypass closure, thereby causing the bypass closure to be held in the closed position. Accordingly, fluid pressure, depending on the direction of flow is exerted against generally opposite sides of the bypass closure, thereby maintaining it in the closed or the open position.
To facilitate repeatable movement of the bypass closure, means are provided that define a guide path for bypass the closure. The bypass closure includes an extension protruding therefrom that is slidably received in the guide path. During operation, the extension travels within the guide path as the bypass closure moves generally rectilinearly between the open and the closed positions.
In the preferred embodiment of the present invention, a bypass cover is coupled to the valve body and defines, at least in part, the above-described guide path. Preferably, the guide path is in the form of a bore extending partway through the bypass cover. It is also preferable that the bypass cover be threadably attachable to the valve body.
The present invention also resides in the bypass closure being configured so as to prevent fluid, usually in the form of refrigerant, from being trapped in the guide path as the bypass closure moves between the open and the closed positions. To accomplish this the extension includes at least one radially projecting lobe, and preferably a plurality of such lobes formed so that the outermost edges thereof circumscribe a shape substantially equal to the cross-sectional shape of the guide path. In this manner, gaps between successive lobes allow fluid to escape from the guide path during movement of the bypass closure.
In most applications, the fluid passing through the expansion valve of the present invention will be refrigerant having a first density when in liquid form. It is preferable that the bypass closure be formed from a material defining a second density substantially equal to the first density. By using such a material, and since the bypass closure is nearly completely surrounded by refrigerant, the forces of gravity are neutralized by buoyancy. As such, the forces required to move the free floating bypass closure will only have to be of a magnitude sufficient to overcome any friction forces present. Therefore, the expansion valve can be oriented in any manner as the bypass closure is approximately completely surrounded by refrigerant when in the closed position.
An advantage of the present invention is that by employing a bypass closure configured as described above any refrigerant trapped in the guide path is easily displaced and does not become trapped behind the bypass closure thereby causing potential valve malfunctions.
Another advantage is that by employing a bypass cover that is threadedly mounted to the valve body and defines the guide path, difficult machining and fixturing of the valve body to form the guide path can be avoided.
Yet another advantage of the present invention is that by employing a bypass closure having substantially the same density as the liquid refrigerant, the valve can be positioned in any orientation without effecting its operation.